Traditional color laser printers have a plurality of a removable toner cartridges disposed therein for providing a supply of differently colored toners. The removable toner cartridges include photoconductive drums rotatably supported in cleaner housings. Each of the toner cartridges also include a developer roller rotatably supported in a developer housing coupled to the cleaner housing. The developer rollers transfer toner from the developer housings to the photoconductive drums, when both are rotating, to print a latent image on a recording marking material receiving part.
The developer roller and the photoconductive drum are sometimes coupled to independently rotated gear assemblies. If the photoconductive drum is not properly engaged, it will remain stationary. If the developer roller rotates while the photoconductive drum is stationary, toner developed on the developer roller will be forced from the developer roller and out of the print cartridge. This uncontrolled release of toner, or toner dump, results in failure of the printing operation. If possible, the dumped toner must then be painstakingly removed from the system before the printing operation can be resumed. In some cases, the toner dump may be so extensive as to render further operation of the printing system impractical.
In order to detect rotation of the photoconductive drum, and subsequently prevent toner dump, a number of traditional systems have been developed to measure the torque and current used by the motor circuit that rotates the photoconductive drum. These traditional methods for detecting the rotation of the photoconductive drum are often difficult to implement due to the variation of motor loads across a number of different environments. In addition, such systems include additional sensors, which add expense and complication to the system.